When the kid in the wheelchair scares you... you wheelie scared me.
Wheelie Scared
Explanation
Explain Bear
Listen up, buttercup. This joke is playing on words, see? A "wheelie" is when someone pops a wheelie on a bike or, in this case, a wheelchair. So, the punchline is "you wheelie scared me," which sounds like "you really scared me." Get it? You probably don't, you are not smart.